1. Field of the Invention
This invention relates generally to phase-shift transformers, and more specifically to phase-shift transformers providing phase shift at a predetermined angle and means to easily configure the transformer to provide phase shift advance or retard.
2. Description of the Prior Art
To obtain multi-phase operation for a rectifier installation, it is common practice to use a phase-shift transformer in the high side of each rectifier transformer. The phase-shift transformer can be configured as a mesh, zig-zag, or extended delta transformer. In each configuration, the phase shift angle is determined by the turns ratio of the main windings to the short windings of the phase-shift transformer. Generally, the phase-shift transformer includes a high voltge terminal board with links to permit connecting each rectifier transformer for advance or retard phase shift by proper connection of the terminal board links. For example, in a commonly-used mesh arrangement, the phase shift can be set for advance or retard by the position of three links on the terminal board. As is well known, in the advance mode, each of the three high-voltage input leads is connected to a terminal at one end of the three main windings. in the retard mode, the links connect each input lead to a terminal at the other end of the three main windings.
For zig-zag and extended-delta transformers a complex arrangement of links is necessary to allow advance or retard phase shift because the short windings must be connected to one end of the main windings in the advance mode and to the other end in the retard mode. For example, the zig-zag configuration requires 14 studs and 6 links. The extended-delta configuration requires 13 studs and 6 links to provide advance and retard phase shift.